Vehicle wheel speed sensor assemblies used in conjunction with a vehicle anti-lock braking system often protect the sensor coil and magnet from the elements by enclosing them within a bearing seal or end cap. Occasionally, however, the sensor needs to be removed and serviced, which necessitates removing the seal and exposing the interior of the bearing. Therefore, a new type of sensor assembly has been proposed in which the sensor can be removed for service without breaking the bearing seal. As disclosed in coassigned U.S. Pat. No. 4,988,220 to Christiansen et al, the sensor (48) consists of a coil and magnet that are protected by being molded together into a water tight ring shaped housing (54), which in turn press fits removably over a seal casing. Specifically, the housing (54) press fits over a rubber sleeve (42) molded over the outside of seal casing (28). The same rubber sleeve (42) that retains the sensor (48) also covers slots (38) that are cut into the steel seal casing (28). Therefore, removal of the sensor (48) does not break the bearing seal.
The only drawback of the serviceable design described above is that the same rubber sleeve and plastic housing that provide protection and removability also serve to magnetically insulate the exciter ring from the magnet and coil. This can reduce the strength and efficiency of the system, just as insulation would in an electrical circuit or a heat conduction path. A stronger magnet would have to be used to overcome the resistance. Also, the sleeve (42) has a lip (44) which, while it retains the sensor (48) securely, could potentially be damaged during its removal.